1. field of the Invention
The present invention relates to an improved prepupillary lens which may be surgically implanted in a human eye and more particularly to a method for securing on the lens loops which anchor the lens in the eye.
2. Statement of the Prior Art
In the prior art prepupillary lenses have been used in an operation for surgically implanting a lens on the iris of a human eye. Cornelius D. Binkhorst, M. D. , who has performed this operation since 1958, has used a two-loop lens and a four loop lens. He has described both of these lenses in an article entitled, "The Iridocapsular (Two-loop) Lens and the Iris-clip (Four-loop) Lens in Pseudophakia", which he wrote for the 1973 September-October edition of Transactions of the American Academy of Ophthalmology and Otolaryngology. These lenses are made from a plastic material, polymethyl methacrylate, which is commonly used to make contact lenses. The lenses are in the shape of a plano convex lens and have a diameter of 5.0 millimeters and a central thickness of from 0.5 millimeters to 0.6 millimeters depending on the required lens strength. In the human eye both lenses are located in front of the pupil near the iris and are anchored by wire loops.
Before inserting a four-loop lens into the eye an intracapsular cataract extraction is performed. The four-loop lenses have one pair of anterior loops formed from 0.15 millimeters Supramid wire lying on the front of the iris and one pair of posterior loops formed from 0.2 millimeters Supramid wire or 0.15 millimeters platina-iridium wire lying just behind the iris. The clearance between the anterior loops and the posterior loops on each side of the lenses is from 0.5 millimeters to 0.75 millimeters. The overall length of the four-loop lens measured from the curved portion of one anterior loop to the curved portion of the other anterior loop is from 7.5 millimeters to 8.0 millimeters and measured from the curved portion of one posterior loop to the curved portion of the other posterior loop is from 8.5 millimeters to 9.0 millimeters. Both the anterior and posterior loops are bent backwards with the loops having a radius of curvature of approximately 30 millimeters. The four-loop lenses clip onto the front and back of the iris diaphragm and the posterior loops and the anterior loops are tied together with suture.
Before inserting a two-loop lens into the eye an extracapsular cataract extraction, which leaves the iridocapsular membrane, is performed. The two-loop lenses are identical to the four-loop lenses with the single exception being that there are no anterior loops. The posterior loops are buried in the iridocapsular membrane.
It is well known that the method of fixing the lens in the eye determines the contact the lens makes with the eye and is decisive to the success of the lens implant. Fixation on the iris diaphragm alone is not a complete fixation because the lens implant, being subject to gravity and centrifugal forces, has a tendency to move about within the eye. Fixation on the rigid iridocapsular membrane diaphragm is a complete fixation. Only the two-loop lens can be affixed to the iridocapsular membrane diaphragm and it is therefore preferred over the four-loop lens.
The present method used to secure the posterior loops on the lenses involves the drilling of four holes adapted to slideably receive the prongs of the posterior loops and disposed perpendicularly to the planar surface of the plano convex lens extending through to the convex surface, the threading of a prong into one of the four holes, the flattening of the end of the prong, and the pulling the flattened end back through the hole thereby enlarging the hole forming a cavity on the convex surface and securing the the flattened end within the hole. The cavities on the convex surface collect organic foreign bodies such as bacteria and inorganic debris in them thereby irritating the eye. In addition the prongs are not as secure as they should be and may become detached from the lens both during the implanting operation or after the lens has been implanted causing serious damage to the eye or they may be pushed out past the convex surface and subject the part of the eye in front of the lens to irritation and possibly to injury.
The prior art lenses can be better understood by reference to FIGS. 1, 2, 3 and 4. Referring to FIG. 1 in which a perspective view of the two-loop lens is shown a two-loop lens 10 has an optical member formed from polymethyl methacrylate and has a convex surface 11 and a planar surface 12. A pair of posterior loops 13, each having prongs 14 fixedly joined to the lens 10. Referring to FIG. 2 in which a top plan view of the two-loop lens 10 is shown the lens 10 has a set of four holes 15 disposed perpendicular to the planar surface 12 and extending through to the convex surface 11. FIG. 3 is a cross-sectional view of the two-loop lens 10 and shows the ends 14a of the prongs 14 flattened and the holes 15 have been enlarged to form cavities 15a and to secure the flattened ends 14a in the holes 15. FIG. 4a shows prong 14 of the posterior loop 13 after it has been inserted into the hole 15 on the side of the planar surface 12 and extending past the convex surface 11. FIG. 4b shows the end 14a of the prong 14 after it has been flattened. FIG. 4c shows the prong 14 after it has been pulled through the hole 15 with its flattened end 14a enlarging the hole 15 to form a cavity 15a on the convex surface 11. This method of securing the posterior loops 13 may be used with loops made from Supramid wire or platina-iridium wire.